So, I got to try the Malanththrope in a few games and can say without hesitation that it is easily one of the best support units available to not only Nids, but any army.
For a paltry points investment, you get a unit that makes the test of your army infinitely more resilient and that provided synapse and that fights fairly well, too. Mine have helped to finish off units in fights and then gone on to give everyone in 12″ Preferred Enemy due to prey adaptation! Nice! With their high strength and posion attacks, they can take on vehicles and infantry.
Being resilient, they are able to run solo, too, allowing you to spread out your shrouded bubble more so than with Venomethropes, and then advance up the field with your assault forces.
In both games I played, they were all star units and I can already say that I won’t write a list without at least one, probably two of them.